Solar-Tectic LLC of Briarcliff Manor, NY, USA says that a patent application for a tin perovskite/crystalline silicon (c-Si) thin-film tandem solar cell has been granted by the US Patent and Trademark Office (USPTO). US patent 15/205,233, the first for a perovskite layer on crystalline silicon thin-film (tandem cell), covers all non-toxic perovskites and inorganic materials. The inventor is Solar-Tectic’s CEO Ashok Chaudhari.

Recently, perovskite materials have gained attention as a promising solution to the long-standing problem of solar cell efficiency. While there have been reports of perovskite/silicon (wafer) tandem solar cells (and extensive intellectual property), there have been none on a perovskite/crystalline silicon thin-film tandem solar cell. Wafer-sized bottom poly- and monocrystalline silicon layers in PERC, PERL, HIT, HJ or perovskite/silicon tandem cells are typically 200–280μm thick, whereas Solar-Tectic's thin-film crystalline inorganic bottom layers can be as thin as 20–30μm with the same or similar efficiency. Moreover, they can be processed at much lower temperatures, lowering costs of production significantly. The top perovskite layer is less than 1μm (an ultra-thin film) and a thin-film crystalline silicon (CSiTF) bottom layer decouples the need for a silicon wafer. If the price of polysilicon rises – due to tariffs or otherwise – less silicon material use will be an additional cost saving, notes Solar-Tectic.

An example of a perovskite layer is CsSnBr3, which has a bandgap of 1.75eV, ideally suited as a top layer on silicon thin-film (which has a bandgap of 1.12eV). Such a tandem solar cell is capable in theory of 45% efficiency, although Solar-Tectic has set a more realistic 30% efficiency goal, higher than the best silicon wafer technologies such as PERC, PERL, HIT and HJ cells with 25–26.6% efficiencies. The efficiencies of existing solar cells on the market generally range from 14–25%. A cost-effective 30%-efficient solar cell with a simple design could revolutionize the solar energy industry by dramatically reducing the balance of system (BoS) costs, eliminating the need for fossil fuel generated electricity entirely, reckons Solar-Tectic, and silicon wafer technology based on polycrystalline or monocrystalline silicon (90% of today’s market) would become obsolete.

Solar-Tectic says that its entire process is environmentally friendly, since non-toxic tin (Sn) is used to deposit the crystalline silicon thin-film material for the bottom layer in the tandem configuration as well as in the top, perovskite layer. The more commonly used toxic lead (Pb) is not used in the perovskite here. The processing methods are conventional and similar to those used in the existing thin-film solar cell industry, as well as in the display industry, notes the firm.

The tin perovskite/silicon thin-film tandem solar cell is part of a ‘Tandem Series’ of high-efficiency and cost-effective solar cells by Solar-Tectic with the potential to surpass the efficiencies of thin-film solar cell technologies such as cadmium telluride (CdTe), copper indium gallium diselenide (CIGS) and amorphous silicon (a-Si) and to replace incumbent silicon photovoltaic technology based on poly and monocrystalline wafers, says the firm. Solar-Tectic’s solar cell technologies include a variety of different proven semiconductor photovoltaic materials (i.e. III-V, CZTS, a-Si, etc) for the top layer on a silicon (or germanium) bottom layer, on various substrates including flexible glass and polyimide for R2R (roll to roll) processing.

Recently, a patent for a germanium perovskite thin-film solar cell was also granted to Solar-Tectic and last year a similar patent was issued for a ‘Hybrid Organic/Inorganic Eutectic Solar Cell’, which is applicable to organic light-emitting diodes (OLEDs).

R&D on the new perovskite thin-film tandem technology has begun at Blue Wave Semiconductors Inc in Maryland, USA under the direction of Dr Ratnakar D. Vispute.

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